The present invention relates generally to pulse count positioning systems and more particularly to a method of measuring current levels and pulses that correspond with positions of an electric device such as an automotive accessory.
The position of electric devices such as motorized automotive accessories for climate control air handling, seat positioning, mirror positioning, and sunroof operation, among others, is generally controlled by an electric motor in communication with the electric device. Often, the position of the electric device must be known in order to facilitate certain features such as seat memory or safety functions such as stopping and/or reversing movement of a power sunroof when an obstruction is present. Methods of determining the position of the electric device include individual potentiometers mounted to the electric device that generate an electrical signal corresponding with position information, or more prevalently, pulse count positioning systems that count commutation pulses of the electric motor.
Pulse count positioning systems are well known in the art and generally determine the position of an electric device, e.g., automotive accessory, by counting the number of commutation pulses generated by the electric motor powering the device. As the electric motor rotates, current through motor windings is periodically interrupted as motor brushes rotate between poles of the motor. As a result, pulses or spikes in the current are produced, which are commonly referred to in the art as commutation pulses. Since the electric motor has a fixed number of poles, and each revolution of the motor causes the device to move a known distance, the position of the device may be correlated to the number of commutation pulses generated by the motor. Accordingly, the position of a device may be determined without the need for additional components such potentiometers or switches as previously implemented in the known art.
One such pulse count positioning system is disclosed in U.S. Pat. No. 5,497,326 to Berland et al., wherein a control system and method to move a motorized vehicle accessory a distance from a first position to a second position is disclosed. The control system comprises a controller that includes a routine for developing an adjustment factor, which modifies an output signal to correct for inaccuracies in detection as a result of memory drift over time. Additionally, commutation waveforms are analyzed to determine when an obstruction is present such that certain safety features of the system may be employed to stop the motor when an obstruction is detected. Unfortunately, the system of Berland does not filter pulses that result from a variety of motor conditions that include by way of example, motor backup due to cogging and/or gear train affects, in which pulses normally continue to be generated. Such pulses, when counted, contribute to errors in determining the position of the electric device or vehicle accessory.
Accordingly, there remains a need in the art for a method of measuring current in a pulse count positioning system that filters and analyzes commutation pulses based on a variety of motor conditions that include, for example, motor backup due to cogging and/or gear train affects.
In one preferred form, the present invention provides a method of measuring current in a pulse count positioning system, wherein current flow through an electric motor is measured at regular intervals, summed at intervals that correspond with the regular intervals, and stored as a pulse occurs. Once the measurements are stored, a new sum of the current flow is initiated. Further, current flows for a previous two sums are compared after a maximum timeout. Based on the comparison, the method of the present invention takes into account various motor conditions such as backup due to cogging and/or gear train affects, which may or may not cause a pulse to be detected, in arriving at a total current pulse count. Accordingly, various motor conditions are analyzed before arriving at the total current pulse count for a more accurate determination of the position of an electric device.
After the sums are initially compared, rules are employed to increase or decrease the pulse count by a value depending on the sum comparison, which correspond with various cogging force and/or gear train situations of the electric motor. Accordingly, the current sum between the previous two pulses is compared with the current sum when an actuator ceases using the maximum timeout as the detection for the end of an associated drive. The total current pulse count is then correlated with the position of an electric device or vehicle accessory, such as an air directing door in an automotive climate control system, in the preferred form of the present invention.
In another form, a system for measuring current is provided that comprises a signal processing system that receives current pulses from an electric motor, an A/D converter that measures the current pulses at regular intervals, a microcontroller that sums the current pulses at a second interval, a timer in communication with the microcontroller that sets time for the intervals, and a host microcontroller in communication with the microcontroller. Accordingly, the microcontroller transmits information to the host microcontroller on how an actuator for positioning a device should be positioned based on the current measurements.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.